In switching regulators, it is often desirable to measure the input current coming into or being supplied to the regulator during operation. This is particularly true when batteries are being used as the power source and the amount of discharge current out of the batteries needs to be monitored and/or limited to, for example, improve the life of the batteries. Moreover, customers often have the need to determine the power efficiency of their switching regulators and to do so requires the ability to monitor the input voltage Vin, input current Iin, output voltage Vout, and output current Iout of the regulator. The power efficiency of a switching regulator is given by the output power Pout provided by the regulator divided by the input power Pin supplied to the regulator (Pout/Pin), where Pout=lout×Vout and Pin=lin×Vin. While customers would like to be able to determine power efficiency, they do not want to significantly increase the cost or complexity of their regulators to do so. Input voltage Vin, output voltage Vout and output current Iout are all presently monitored in most switching regulators. Input current Iin, however, is not typically monitored and needs to be in order to enable the power efficiency to be determined. As will be appreciated by those skilled in the art, the input current Iin to a switching regulator is a pulsed current and is not a direct current (DC) signal that is easily measured.
The output current Iout from a switching regulator can be sensed using a sensing element, such as the low side of a metal oxide semiconductor field effect transistor (MOSFET) switch in the regulator, or using a DC resistance (DCR) of an output inductor or a current sense resistor in series with an output switch, as will be appreciated by those skilled in the art. FIG. 1 is a schematic and functional block diagram of a typical switching regulator 100 having a Buck converter topology and emphasizing the output section of the regulator. A control section 110 of the regulator is not shown in detail, but typically includes an error amplifier with feedback components, a pulse width modulator circuit, and level shifters to translate pulse width modulated signals PWM1, PWM2 generated in the control section to levels suitable for the control of two driver circuits 125 and 130, as will be appreciated by those skilled in the art. In response to the PWM1 and PWM2 signals, the driver circuits 125 and 130 develop an upper gate signals UGATE and lower gate signals LGATE, respectively, that are applied to control the switching of an upper gate NMOS transistor M1 and lower gate NMOS transistor M2. The UGATE and LGATE signals are complementary signals to operate the transistors M1 and M2 operate in a complementary manner, meaning when the UGATE signal is active to turn ON transistor M1 the LGATE signal if inactive to turn OFF transistor M2, and vice versa. The transistors M1 and M2 are connected to one end of an inductor LF at a phase node PH, with the other end of the inductor developing an output voltage Vout across a load that is represented by a capacitor CF and resistor RL. The control section 110 receives a current feedback signal indicating the value of an output current Iout flowing through the inductor LF and a voltage feedback signal indicating the value of an output voltage Vout developed by the switching regulator 100.
In operation, the control section 110 develops the pulse width modulated signals PWM1, PWM2 responsive to the current and voltage feedback signals to control the switching ON and OFF of the driver circuits 125 and 130. In response to the PWM1 and PWM2 signals, the driver circuits 125 and 130 alternatively activate the transistors M1 and M2 to provide either a boot voltage on the phase node PH when the transistor M1 is activated (and transistor M2 is deactivated) or to provide a reference voltage (ground in the example of FIG. 1) on the phase node when the transistors M2 is activated (and transistor M1 is deactivated). Power is supplied to the load and stored in the inductor LF when the transistors M1 and M2 are ON and OFF, respectively, and is transferred from the inductor to the load when the transistors M1 and M2 are OFF and ON, respectively, as will be understood by those skilled in the art. The PWM1, PWM2 signals have an associated duty cycle that determines how long each transistor M1, M2 is turned ON and OFF during a corresponding cycle and in this way determine the value of the generated output voltage Vout. The control section 110 controls the duty cycle of the PWM1, PWM2 signals responsive to the voltage feedback signal so that the desired output voltage Vout is generated.
A current sensing element senses the output current of the switching regulator 100 that flows through the load and generates the current feedback signal indicating the value of this current. The control section 110 also sense the output voltage Vout across the load as previously discussed. The input voltage Vin is also known in the conventional switching regulator 100. Moreover, the input current Iin, which corresponds to the current flowing into the transistor M1, can also be and is sensed in some conventional switching regulators. From these sensed parameters, namely input current Iin, input voltage Vin, output current Iout, and output voltage Vout, the control section 110 can calculate the efficiency of the switching regulator 100.
Sensing of the input current Iin, however, requires additional circuitry such as a dedicated sense element like a sense amplifier, sense resistor, or current sense transformer and additional circuitry in the control section 110. The input current Iin is a pulsed current signal and an average value must be determined for use in calculating power efficiency, with this average value being based upon the magnitude and duty cycle of the input current. This additional circuitry increases the cost of the switching regulator 100, occupies valuable space in an integrated circuit in which the switching regulator or portions thereof are typically formed, and increases the cost of the regulator.